# which adduser
which: no adduser in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.4.3)
$ which adduser /usr/sbin/adduser $ equery belongs `which adduser` [ Searching for file(s) /usr/sbin/adduser in *... ] sys-apps/shadow-4.1.2.2 (/usr/sbin/adduser -> useradd)